Technical Abstract:
The efficacy of Isaria fumosorosea (= PFR 97®) on the leaf phylloplane over time for controlling Madeira mealybug nymphs before shipping plant products was assessed under laboratory conditions. Hibiscus leaves were dipped into beakers filled with 0, 1, 2, 4, 8, and 10 g of PFR 97® / L of water and tapped on brown paper towels to allow excess suspension to run off. Damp leaves were individually placed into empty plastic Petri dishes and a single 3rd - 4th-instar mealybug was exposed on the leaf. Each dish bioassay was sealed and placed in an environmentally controlled chamber at 25 °C under a 14 h L: 10 h D photoperiod. Percent mortality was determined after observing nymphs daily for 8 days post - exposure. The LT50 of nymphs after exposure to these dilutions varied from 6.9 – 11.1 days. Mortality of the mealybugs for concentrations 2, 4, 8, and 10 g / L was > 50% after 7 days post - exposure to PFR 97, but increased to 100% after final molting to the adult stage. The results suggest that molting may remove infective spores from penetrating the exoskeleton and subsequently decrease efficacy of the fungal treatments until the adult stage. Results have demonstrated there is potential for using I. fumosorosea as part of a strategy for mitigating and controlling mealybug populations on plants pre - and post – shipping.